Response teams were deploying remote-operated submarines in an urgent effort Sunday to stop the flow of oil from the site of the accident in the Gulf of Mexico that destroyed the BP-leased rig, the Deepwater Horizon.

If the gambit fails, it could take months to stop the leak—now estimated at 1,000 barrels (42,000 gallons/160,000 liters) per day of crude oil, according to the joint U.S. government and oil industry task force.

Although the oil is not flowing directly from the well, but from the damaged rig pipes, and is therefore being released at a somewhat constrained rate, the effort to stop it will be complex and difficult, response team members said at a news conference.

Many of the best-known oil spills in history have resulted from tanker accidents, with the release of oil near the water surface. In contrast, this leak is nearly 5,000 feet (1,500 meters) beneath the surface, where pressure is extreme.

The best hope is that the remote-operated submarines—at least four are deployed at the scene--would be able to activate a huge device on the sea floor called a “blow-out protector,” a series of valves meant to control pressure in the well. “This is a highly complex operation,” said Doug Suttles, chief operating officer for BP’s exploration and production division. “And it may not be successful.”

If that operation fails, the next option is to drill a relief well—a process that would take at least two to three months, said Suttles. A BP rig equipped for this task is to arrive at the scene by Monday.

Suttles also said that the company was putting in place a plan to mitigate the potential damage by capturing the oil beneath the water surface. It’s an operation that involves lowering a large dome to trap the oil and pipe it to a holding vessel at the surface.

Although such a system was deployed successfully after Hurricane Katrina, Suttles said it has never been attempted at this depth. “We have the world’s best experts working to see if we can make that possible,” he said.

The task force does not know how long the oil has been flowing from the damaged pipe nor how much has spilled. But at the current rate, it would be less than three days before becoming characterized by federal authorities as a major spill—greater than 2,381 barrels (100,000 gallons/380,000 liters).

Gulf Coast States on Alert

Although still small compared to the worst oil spill in U.S. history, the Exxon Valdez disaster of 1989, in which 11 million gallons (42 million liters) were released, concern was high regarding potential impact onshore.

Rear Admiral Mary Landry, commander of the Eighth U.S. Coast Guard District, who is leading the response effort, said state and federal agencies all along the Gulf Coast were on the alert, and Louisiana had already begun to deploy containment boom to protect environmentally sensitive areas. But she said no landfall was expected within the next 72 hours; authorities are hesitant to forecast the direction of the spill beyond that due to changeable wind and weather.

“But our goal is to fight this as far offshore as possible,” she said.

Landry said that chemical dispersant also has been applied to the oil spill, and that the team was ready to apply more. She said a third of the world’s oil dispersant supply was available in the Gulf region.

According to the U.S. National Research Council, oil spill dispersants do not actually reduce the total amount of oil entering the environment. Rather they change the chemical and physical properties of the oil, making it more likely to mix into the water column than to contaminate the shoreline. “Dispersant application thus represents a conscious decision to increase the hydrocarbon load … on one component of the ecosystem… while reducing the load on another,” a 2006 NRC report said.

But both skimming and dispersant operations on the surface were hampered by bad weather Sunday, with sea swells as high as 7 feet (2 meters.) The underwater submarine operations were unaffected by the weather, however, but were expected to take at least a day.

One of the worst oil spills to impact the Gulf was also a well blowout, in the Bay of Campeche off Ciudad del Carmen, Mexico, in June 1979. By the time the well was brought under control nearly nine months later, 140 million gallons ( 530 million liters) of oil had been released into the bay. The spill, which eventually fouled the Texas coast, was the second largest oil disaster of all time—surpassed only the deliberate release of oil in the Gulf War in January 1991.

The well mishap occurred just as the U.S. Senate was prepared to unveil a major proposal to expand offshore oil production—as part of larger legislation aimed to address global warming. At the event, which had been scheduled for Monday, the bill’s sponsors had planned to appear at the podium flanked with industry supporters, including from BP.

But the bill’s advocates have been saved the discomfort of such a joint appearance while the Gulf spill response is underway. Due to a political squabble over immigration reform, the Senate energy and climate change bill is now on hold.